The present disclosure relates to self calibration. In particular, it relates to self calibrating conformal (non-flat) phased arrays.
Large phased arrays on airborne platforms suffer from continuously changing flexure that will degrade the generated beam patterns. Generally, there are two standard approaches to measure array flexure. The first approach is a mechanical approach that involves embedding a mesh of mechanical sensors across the array to measure strain and mechanical movement of the array. The second approach is a radio frequency (RF) approach that involves measuring the beam pattern externally and, from those measurements, inferring the element movement across the array.
The first approach, the mechanical approach, is quite expensive and requires a very complex calibration phase to turn mechanical strain readings into element movement. Also, the mechanical approach relies on embedding mechanical sensors within an electronic substrate, which is a difficult integration task. In addition, global errors from local strain readings increase as the array size increases. Additionally, without feedback generated from the actual beam pattern, this approach can drift out of calibration.
The second approach uses externally mounted horns or antennas to receive a calibration transmission from the array at certain angles. From these measurements, beam pattern anomalies can be detected and some phase corrections may be attempted. However, without a detailed knowledge of the spatial pattern at many simultaneous points, it is impossible to estimate flexure across the array to any great degree of precision. Because of the limited positions in which an external antenna could be mounted on an aircraft within viewing angles of the conformal array, this greatly limits the ability to do in-flight calibration and flexure estimation.